The present invention relates to a digital X-ray radiography method suitable for imaging a large view field such as a chest and an apparatus for realizing same and in particular to a method for correcting image distortion useful for correcting with a high precision image distortion produced in case where an imaging unit such as an image intensifier, etc. is used and an apparatus for realizing same.
As a method for obtaining an X-ray image by imaging a chest several times, dividing it into a plurality of parts, while varying a relative position of an X-ray detecting unit with respect to an a subject body, heretofore there is known a technique described e.g. in "Japanese Journal of Medical Electronics and Biological Engineering", Vol. 31, Special Issue (Proceedings of the 32nd Conference, Japan Society of Medical Electronics & Biological Engineering), p. 209, May 1993. This technique is a method, by which an X-ray television camera consisting of an X-ray image intensifier and a television camera is used as an X-ray detection unit; a subject body to be imaged is standing; an X-ray source is fixed; and the X-ray detection unit is translated parallelly on a straight line in one direction with respect to the subject body, and by which a right and a left lung are imaged separately and an image synthesized by joining two images thus obtained is displayed.
Further, as a method for obtaining an X-ray image in synchronism with a variation in an electrocardiogram, there is known an angiographic technique described e.g. in JP-A-60-50900.
Furthermore, heretofore, it is widely known that a pin-cushion type distortion is produced in an obtained image, in case where imaging is effected by using an imaging unit such as an image intensifier, etc. in a radiography system.
In a radiography system, the pin-cushion type distortion characteristics vary, depending on the distance between an X-ray tube and an X-ray image intensifier. As a technique for suppressing variations in these pin-cushion type distortion characteristics, there is known a technique described in JP-A-2-10636. By this technique variations in the characteristics of the pin-cushion type distortion produced by variations in the distance between the X-ray tube and the X-ray image intensifier are cancelled by controlling potential applied to electrodes disposed in the neighborhood of an output phosphor screen of the image intensifier.
Further, as a method, by which distortion in an image itself obtained by the imaging is not suppressed as by the technique described above but the obtained image is corrected in an electronic manner, there is known a technique described in JP-U-5-28316. By this technique an equidistantly partitioned rectangular chart is imaged; sampling points are manually inputted by means of a digitizing system, a mouse, etc.; a characteristic curve representing the pin-cushion type distortion obtained by starting from distortions at the sampling points is approximated by the minimum square method; and an approximation formula thus obtained is applied to all the points of the image, in which the pin-cushion type distortion exists, to correct the pin-cushion type distortion.